The present invention relates to a gas delivery apparatus for administering a gas to a patient during surgery, and more particularly for delivering anesthetic to a patient during surgery
During surgical procedures, there is a need to anesthetize a patient in order to eliminate, or at least reduce: pain associated with the procedure; and movement of the patient during the procedure. Anesthesia is considered a drug-induced depression of at least a portion of nervous system, or portion thereof, of the patient.
In the sequence of events of drug-induced depression of the central nervous system, there occurs a level of depression that allows the muscles of the pharynx (e.g. the tongue) to relax causing soft-tissue structures to collapse into and obstruct the airway. This happens at an earlier stage than that at which the muscles of respiration (e g the diaphragm) cease to function. In other words, a condition known as xe2x80x9cobstructive apnea,xe2x80x9d where the diaphragm is struggling to pull air through an obstruction of the upper airway occurs before the diaphragm itself ceases to function (xe2x80x9ccentral apneaxe2x80x9d). In this sequential depression of the central nervous system, death occurs from Asphyxia before the drug itself can produce complete depression of the nervous system.
An upper airway obstruction occurs upon the induction of almost every general anesthetic and is a frequent occurrence during the administration of heavy sedation for procedures done nominally under xe2x80x9clocal anesthesia with sedation.xe2x80x9d Under most conditions, the treatment is so routine as to be taken for granted by practitioners skilled in airway management. Manual support of the airway such as with an invasive endotracheal tube, application of a face mask over the mouth and nose and various other airway devices are employed, often with supplemental oxygen.
However, the use of a face mask or an endotracheal tube during surgical procedures has many drawbacks. The standard face mask places pressure on the chin and tends to collapse soft-tissue structures of the oropharynx. Additionally, air pressure that is applied through the face mask tends to equalize through the nose and the mouth, and therefore it can be counter-productive to the supporting of soft tissue to open the airway. Further, using a face mask usually requires one or two additional maneuvers, for example manual support of the chin, the insertion of an oral airway, etc., in order to remedy the problem. None of the invasive airway-support devices currently used in conventional anesthesia practice can be inserted in the conscious patient without causing significant discomfort and/or physiological disturbance.
Furthermore, recent advances in cosmetic surgery have made airway management significantly more challenging and have caused practitioners to accept conditions having a reduced margin of safety for their patients. In particular, laser procedures on the face are requiring heavier sedation leading more often to respiratory depression and obstruction while, at the same time, the increased fire hazard restricts the use of oxygen.
Obstructive Sleep Apnea (OSA), a syndrome defined in the early 1980""s, is similar to drug-induced obstructive apnea in anatomy and treatment. The treatment of OSA has demonstrated that upper airway obstruction occurring during the sleep of afflicted patients can be relieved by the application of positive pressure through the nose alone. OSA differs from drug-induced obstructive apnea in that it is not drug-induced. Further, OSA typically does not have acutely disastrous consequences, but rather has long-term ill-effects and is a chronic condition.
A conventional method for treating a form of OSA is to provide a continuous positive airway pressure (C-PAP) through the nose in order to prevent an upper airway obstruction. Nasal masks are used, as are nasal insert devices. InnoMed Technologies, for instance, provides a device called NasalAire used to treat obstructive sleep apnea. The device includes conical shaped nasal inserts connected to gas delivery tubes which are connected to an air delivery system. A C-PAP generator is included, which automatically increases and decreases air flow rate to maintain a continues positive airway pressure. Furthermore, the device includes vent holes for venting CO2 from the exhaling user.
FIG. 1 illustrates a conventional system for treating sleep induced apnea by providing a continuous positive airway pressure through the nose. As depicted in the figure, the patient 104 is fitted with tubing 102. The tubing 102 receives airflow from a C-PAP machine and administers the airflow to the nose of the patient by tube branches 106. An airflow delivery device 108, having nasal inserts 110 is placed such that nasal inserts 110 are disposed within the nasal vestibules 114 of patient 104. Airflow delivery device 108 additionally includes ventilation holes 112, which provide ventilation for CO2 from the user during expiration. Examples of such devices are disclosed in U.S. Pat. No. 5,533,506 to Wood, U.S. Pat. No. 4,702,832 to Tremble et al, and U.S. Pat. No. 5,134,995 to Gruenke et al., the entire disclosures of which are incorporated herein by reference.
What is needed is a method and apparatus for preventing complete airway obstruction of a patient when the patient is deeply sedated after induction of anesthesia.
What is additionally needed is a method and apparatus for enabling a patient to adequately respire at surgical levels of anesthesia without an invasive airway and manual or mechanized ventilation.
What is additionally needed is a method and apparatus for cost-effectively adding air to the anesthetic gasses for reducing the risk of combustion in the surgical field when using cautery or laser devices.
What is additionally needed is a method and apparatus for preventing leakage of the anesthesia to the operating room.
What is additionally needed is a method and apparatus for more accurately monitoring spontaneous respirations in a pressurized system.
What is additionally needed is a method and apparatus for preventing an airflow generator from excessively pressurizing an anesthesia circuit.
What is additionally needed is an apparatus that is: operably connectable to an existing anesthetic delivery apparatus; operable to prevent complete airway obstruction of a patient when the patient is deeply sedated after induction of anesthesia; and operable to enable a patient to adequately respire at surgical levels of anesthesia without an invasive airway and manual or mechanized ventilation.
It is the object of this invention to provide a method and apparatus that may comfortably be applied to the conscious patient prior to the induction of anesthesia to prevent airway obstruction and maintain oxygenation after the patient has become unconscious under the influence of anesthesia.
It is another object of this invention to enable a patient to adequately respire at surgical levels of anesthesia without an invasive airway and manual or mechanized ventilation.
It is another object of this invention to cost-effectively add air to the anesthetic gasses for reducing the risk of combustion in the surgical field when using cautery or laser devices.
It is another object of this invention to prevent leakage of the anesthesia to the operating room.
It is another object of this invention to more accurately monitor spontaneous respirations in a pressurized system.
It is another object of this invention to prevent an airflow generator from excessively pressurizing an anesthesia circuit.
Upper airway obstruction caused by a drug-induced depression of the central nervous system is preventable by applying positive pressure through the nasopharynx while leaving the oral cavity open to ambient pressure. The pressure differential thus created, splints the soft tissues out of the airway with a natural pressure relief valve through the oral cavity. The maximum pressure obtainable is consistently sufficient to relieve the obstruction, but is less than the 20 centimeters of water that might send air to the stomach.
In accordance with one method of the present invention, nasal oxygen is applied to an awake patient through a sealed nasal connection. A conventional anesthesia administering apparatus, i.e., anesthesia circuit, that is unable to provide air to a patient may be modified to include an air supply. In any event, a conventional anesthesia administering apparatus can be modified in accordance with the present invention to provide a sealed nasal connection. Nasal oxygen may be applied as 100% oxygen, or a diluted form of oxygen by supplying air.
The sealed nasal connection may be provided by any device that may: be inserted into the nasal vestibule of the patient; provide a seal between the device and an inner surface of the nasal vestibule; and administer an amount of a gas into the nasal vestibule via the nasal vestibular portion, wherein the seal promotes airway pressure buildup that is sufficient to prevent obstruction of the airway during depression of at least a portion of the nervous system and prevents escape of the gas from between the nasal vestibule and the device. For example, the sealed nasal connection may be provided by a device having a nasal vestibular portion that is shaped as portions of the devices as disclosed in U.S. Pat. No. 5,533,506 to Wood, U.S. Pat. No. 4,702,832 to Tremble et al, U.S. Pat. No. 5,134,995 to Gruenke et al., U.S. patent application Ser. No. 09/430,038, the entire disclosures of which are incorporated herein by reference.
Unlike the airflow delivery device 108 discussed above with reference to FIG. 1, the sealed nasal connection of the present invention cannot include ventilation holes. In particular, the ventilation holes 112 of airflow delivery device 108 provide ventilation for CO2 of the user during expiration. However, such vent holes would be counter-productive if included in the sealed nasal connection of the present invention. In particular, such vent holes would enable gas, that would otherwise have been forced into the airway of the patient to prevent airway obstruction, to escape. Accordingly, the ability for the sealed nasal connection of the present invention to prevent airway obstruction would be reduced.
Once nasal oxygen is administered to the awake patient, the patient is forced to breathe in through the nose and out through the mouth. The patient will do so fairly comfortably as long as the nasal oxygen flow rate is adjusted to comfort.
Anesthesia is then induced, either intravenously or inhalationally through the sealed nasal connection. Then, when anesthesia is induced and total relaxation of the pharyngeal muscles occurs, obstruction is prevented automatically as pressure within the anesthetic circuit builds to prop open the patient""s airway. With the mouth left open to ambient pressure in the deeply sedated patient, a pressure gradient is established which allows the soft palate and tongue to be propped out of the pharyngeal airway while at the same time creating a low pressure seal of the soft palate to the tongue which remarkably releases somewhat between 8 and 20 cm of water pressure. There is, in effect, a pressure xe2x80x9cpop-offxe2x80x9d valve that prevents a pressure build-up which would force air into the stomach (20 cm of water is the reported threshold pressure).
Aspiration of gastric acid into the lungs may result in fatal pneumonitis, which is the classic nightmare of anesthesia practice. Over-inflation of the lungs with pharyngeal pressures in excess of 20 cm of water has been shown to blow air into the stomach. The resultant distension of the stomach with air under pressure has been known to cause regurgitation and subsequent aspiration of acid into the lungs. However, C-PAP under 20 cm of water has been shown to oppose the reflux of acid up the esophagus by increasing the intra-thoracic pressure above the intra-abdominal pressure. This serves to create a pressure gradient which opposes reflux under anesthesia.
The reflex apnea triggered by obstruction is prevented and the patient resumes spontaneous respirations after a few seconds of central apnea, which may occur as a consequence to the direct depression of the central nervous system by the anesthetic drug itself.
Deep levels of inhalational anesthesia can be achieved through spontaneous and unassisted respirations. Then, with the sealed nasal connection left in place, anesthesia and oxygenation can be sustained during, for example, a difficult intubation where ordinarily the removal of the oxygen mask would effectively remove adequate oxygenation from the patient. In theory, as long as 100% oxygen is provided at the level of the open vocal chords, even a patient who is not breathing will remain well-oxygenated and viable for nearly an hour. In particular, the patient will maintain adequate ventilation spontaneously when connected to the closed anesthesia circuit with the nasal oxygen flow rate adjusted to maintain a positive pressure sufficient to prevent obstruction. In other words, the patient is enabled to respire adequately, at surgical levels of anesthesia, totally free of an invasive airway and manual or mechanized ventilation.
In accordance with a method of the present invention, a more strict monitoring method is required to detect early partial airway obstruction. For example, a more sensitive anesthetic circuit pressure gauge and a supra-sternal stethoscope may be used. In particular, a conventional pressure gauge in a conventional anesthesia circuit is scaled to approximately 160 units over the full circumference of its face (1 unit=1 centimeter of water pressure). On the contrary, a pressure gauge in accordance with the present invention would be more sensitive and have a scale of 40 units over the same circumference. The fluctuations of the needle of the gauge would, therefore, be amplified by a factor of four making it a sensitive monitor of the alternating pressures of the respiratory cycle. Further, as stated above, because pressures in excess of 20 cm of water has been shown to blow air into the stomach, the pressure gauge must be able to measure at least 20 cm of water. More importantly, the pressure gauge in accordance with the present invention should display the detected pressure at a precision that would readily communicate the difference between a inspiration and an expiration of the patient.
The airway pressure used under anesthesia, in accordance with the present invention, is not C-PAP as applied in the treatment of obstructive sleep apnea. The airflow rate of a C-PAP generator automatically increases and decreases to maintain a constant positive airway pressure. On the contrary, in accordance with the present invention, a gas flow rate to the patient is constant and is manually adjusted to a level that produces a positive pressure, which prevents obstruction. An apparatus in accordance with the present invention is capable of providing a supplemental gas, such as for example oxygen or air, at a constant, adjustable, flow rate to the patient. Using a method in accordance with the present invention, the supplemental gas is supplied in an amount such that there is a constant gas flow rate and there is always a positive pressure, but the magnitude of the pressure varies with respiration. This approach, i.e., using a constant gas flow rate, causes airway pressure to be higher on expiration than on inspiration. The varying pressure and constant gas flow rate provided by the method and apparatus of the present invention is advantageous over conventional C-PAP because the constant gas flow rate and varying pressure promotes a better venous return to the heart. The varying pressure accompanied with the constant gas flow rate in accordance with the present invention is termed alternating positive airway pressure.
The alternating positive airway pressure generated by the system in accordance with the present invention has further beneficial effects. keeps the lungs expanded to a more optimal functional residual capacity, thereby increasing the oxygen reserves within the lungs, which in turn prevents atelectasis from collapse of the alveoli. Further, when air is combined with oxygen, the alternating positive airway pressure generated by the system in accordance with the present invention prevents atelectasis from oxygen absorption. Still further, the alternating positive airway pressure creates a positive intra-thoracic pressure, which serves to reverse any existing tendency towards reflux of gastric contents up the esophagus, which might lead to aspiration into the lungs.
The system and method of use thereof in accordance with the present invention has still further beneficial effects. When inhalational anesthesia is used, the carbon dioxide can be sampled from the scavenger mask to monitor respirations and to assure that the scavenger is working to remove exhaled gas. Depth of anesthesia is rapidly increased by increasing flow rates to the nose so that no exhaled gas comes back into the anesthesia circuit, but rather, is forced out through the mouth. Denitrogenation and oxygenation is facilitated along with the increased flow rate of higher anesthetic gas concentrations into the lungs. Similarly, at the end of the procedure, anesthetic gasses are rapidly eliminated by a unidirectional high flow of oxygen and/or air into the anesthetic circuit. In deep sedation (e.g. MAC, xe2x80x9cMONITORED ANESTHESIA CARExe2x80x9d), precise concentrations of oxygen can be monitored and administered to the patient without escaping into the surgical field thereby reducing the fire hazard that accompanies the routine practice of bringing oxygen into the proximity of cautery and laser devices through a standard oxygen cannula.
Many conventional anesthetic delivery machines or facilities do not have the capacity for adding controlled, pressurized air to the anesthetic gasses. More importantly, no conventional anesthetic delivery machines or facilities have the capacity for adding controlled, pressurized air or pure oxygen to the anesthetic gasses such that the total gas flow rate administered to the patient is sufficient to prevent obstruction of the airway during depression of the portion of the nervous system.
A device in accordance with the present invention includes a constant gas flow rate generator that is adaptable for use with a conventional anesthetic delivery machine. The constant gas flow rate generator will add a gas, such as oxygen or air, at a constant gas flow rate of a level that produces a positive pressure that is sufficient to prevent airway obstruction. Furthermore, a constant gas flow rate generator in accordance with the present invention may include an adjustment device, such as an automatic or manual adjustment device, for adjusting the constant gas flow rate. An exemplary embodiment of an automatic adjustment device includes a gas flow rate meter that is operably connected to a gas flow valve. In particular, in operation of the exemplary embodiment of an automatic adjustment device, the gas flow rate may be set by the user. The gas flow rate may be subsequently monitored by the gas flow rate meter, the output of which controls the gas flow valve to open/close in the amounts required to maintain the gas flow rate set by the user. An exemplary embodiment of a manual adjustment device includes a gas flow rate meter that displays a gas flow rate to a user and a gas flow valve. In particular, in operation of the exemplary embodiment of a manual adjustment device, the gas flow rate as displayed by the gas flow rate meter is monitored by the user. The user will then operate the gas flow valve to open/close in the amounts required to maintain the gas flow rate desired by the user.
A gas delivery apparatus according to the present invention includes a nasal insert having a gas passage therein for insertion into the nose, such as for example a device disclosed in U.S. application Ser. No. 09/430,038, which is capable of forming a seal with the inner surface of the nasal vestibule. Bendable tubing is included in the apparatus. The bendable tubing has a proximal portion connected to the nasal vestibular portion so as to be in gas communication with the gas passage of the nasal vestibular portion. The nasal vestibular portion flares outwardly with respect to the gas passage therein.
The nasal vestibular portion may comprise a superior pole for engaging the apex of a nasal vestibule. Further, an inferior pole of the nasal vestibular portion may be provided to engage an inferior nostril rim of the nasal vestibule. The superior pole may be elongated and rounded, and the inferior pole may comprise an angled wedged shape. Thus, the superior pole, lodged in the apex of the nasal vestibule, may be shaped so as to help to direct the inferior pole against the inner surfaces of the nose to push the surfaces outward, thereby sealing.
The nasal vestibular portion may comprise a flexible material. In this case, a thin flap can be provided around the perimeter of the nasal vestibular portion for providing further sealing with the nasal interior.
A second nasal vestibular portion may be provided to connect with the second nostril of a patient. The second nasal vestibular portion also flares outwardly with respect to the connection part. A head strap and/or an ear hook may be connected to the tubing to hold the tubing on the head of the patient.
A nasal plug can also be adapted to close one nostril when only one nasal airway is supplied with gas. The nasal plug may be similar to the nasal airway which comprises a connection part and a nasal vestibular portion, but in this case would have its gas passage blocked, for example by a cap. Alternatively, the cap could include a small opening to receive an oxygen tube to provide oxygen to the nostril.
In general, the present invention provides a gas administering method for administering gas to an airway of a patient having a nasal vestibule. The gas administering method is for use with a gas administering apparatus comprising a gas source that is operable to provide gas and a nasal vestibular portion arranged so as to receive the gas from the gas source. Further, the nasal vestibular portion is capable of releasing the gas into the nasal vestibule. The method comprises inserting the nasal vestibular portion into the nasal vestibule, forming a seal between the nasal vestibular portion and an inner surface of the nasal vestibule, administering an amount of a gas from the gas source at a constant flow rate into the nasal vestibule via the nasal vestibular portion, and administering an anesthetic to the patient. The anesthetic induces depression of a portion of the nervous system of the patient. Furthermore, the seal causes airway pressure buildup that is sufficient to prevent obstruction of the airway during depression of the portion of the nervous system and prevents escape of the gas from between the nasal vestibule and the nasal vestibular portion.
In one embodiment of the present invention, the gas administering method further comprises administering oxygen into the nasal vestibule via the nasal vestibular portion, prior to the administering of the anesthetic. More particularly, the oxygen is provided from a source of gas that is 100% oxygen. Alternatively, the oxygen is provided from a source of gas that is a mixture of oxygen and nitrogen.
In another embodiment of the present invention, the administering of an amount of a gas comprises administering 100% oxygen.
In another embodiment of the present invention, the administering of an amount of a gas comprises administering air.
In another embodiment of the present invention, the gas administering method further comprises detecting for an airway obstruction. More particularly, the detecting for an airway obstruction comprises placing a stethoscope over the trachea at the supra-sternal notch.
In another embodiment of the present invention, the gas administering method further comprises monitoring respiratory effort. More particularly, the monitoring respiratory effort is performed via an electrocardiogram monitor operating in a thoracic impedance mode.
In another embodiment of the present invention, the gas administering method further comprises retrieving anesthetic that is expired from the mouth of the patient. More particularly, the retrieving waist anesthetic comprises placing an anesthetic retrieving device over the face of the patient.
In general, the present invention further provides a gas administering method for administering a gas to an airway of a patient having a nasal vestibule. This method is for use with a gas administering apparatus comprising a gas source that is operable to provide gas at a constant flow rate and a nasal vestibular portion having a shape such that the nasal vestibular portion provides an outward force on an inner surface of the nasal vestibule, due to elasticity of the nasal vestibule, for retaining the nasal vestibular portion in the nasal vestibule. Further, the nasal vestibular portion is arranged so as to receive the gas from the gas source. Still further, the nasal vestibular portion is capable of releasing the gas. The method comprises inserting the nasal vestibular portion into the nasal vestibule thereby forming a seal between the nasal vestibular portion and an inner surface of the nasal vestibule, administering an amount of a gas at a constant flow rate into the nasal vestibule via the nasal vestibular portion, and administering an anesthetic to the patient. The anesthetic induces depression of a portion of the nervous system of the patient. Finally, the seal causes airway pressure buildup that is sufficient to prevent obstruction of the airway while under sedation and prevents escape of the gas between the nasal vestibule and the nasal vestibular portion.
In general, the present invention still further provides a gas administering method for administering gas to an airway of a patient having a nasal vestibule. This method is for use with an anesthetic administering apparatus comprising an anesthetic gas source that is operable to provide an anesthetic. The method comprises fastening a nasal vestibular portion to the anesthetic administering apparatus so as to receive the anesthetic gas from the anesthetic gas source (the nasal vestibular portion is capable of releasing the anesthetic gas into the nasal vestibule), inserting the nasal vestibular portion into the nasal vestibule, forming a seal between the nasal vestibular portion and an inner surface of the nasal vestibule, fastening a supplemental gas source to the anesthetic administering apparatus (the supplemental gas source is operable to provide a supplemental gas at a constant flow rate to the anesthetic administering apparatus) administering an amount of the supplemental gas from the supplemental gas source at a constant flow rate into the nasal vestibule, from the anesthetic administering apparatus, via the nasal vestibular portion, and administering an amount of the anesthetic gas from the anesthetic gas source into the nasal vestibule, from the anesthetic administering apparatus, via the nasal vestibular portion. The anesthetic gas comprises an amount of anesthetic sufficient to induce depression of at least a portion of the nervous system of the patient. Finally, the seal promotes airway pressure buildup that is sufficient to prevent obstruction of the airway during depression of the at least a portion of the nervous system and prevents escape of the anesthetic gas or the primary gas from between the nasal vestibule and the nasal vestibular portion.
In general, the present invention still further provides a gas administering system for administering gas to an airway of a patient having a nasal vestibule. The gas administering system comprises a gas source that is operable to provide gas at a constant flow rate and a nasal vestibular portion arranged so as to receive the gas from the gas source. The nasal vestibular portion is capable of releasing the gas into the nasal vestibule and is shaped to form a seal between the nasal vestibular portion and an inner surface of the nasal vestibule such that the gas released into the nasal vestibule causes airway pressure buildup sufficient to prevent obstruction of the airway during depression of at least a portion of the nervous system. Further, the seal prevents escape of the gas from between the nasal vestibule and the nasal vestibular portion.
In one embodiment of the present invention, the gas source comprises a primary gas source for providing a primary gas and a supplemental gas source that is operable to provide a supplemental gas. More particularly, the primary gas source may comprise an anesthetic gas providing device. Further, the primary gas source may comprise an oxygen providing device. Still further, the supplemental gas source may comprise an air providing device having a flow rate adjustment mechanism.
In another embodiment of the present invention, the gas administering system further comprises a respiration monitor.
In another embodiment of the present invention, the gas administering system further comprises a scavenging device for scavenging gas expired from the mouth of the patient.
In another embodiment of the present invention, the gas administering system further comprises a gas flow meter for measuring the gas flow rate of the gas provided by the gas source.
Additional advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments of the present invention. The invention itself, together with further objects and advantages, can be better understood by reference to the following detailed description and the accompanying drawings.